Strains of human cytomegalovirus (HCMV), a member of the human herpesvirus family, display genetic variations, and these polymorphisms can be analyzed to study viral transmission, pathogenesis, and evolution. Our laboratory has used restriction fragment polymorphism (RFLP) and polymerase chain reaction (PCR)- based analysis to conduct detailed studies of HCMV transmission among young children. Recently, short tandem repeat (STR) length polymorphisms were identified in the HCMV genome. Davis and colleagues found at least 24 regions that exhibited length or sequence STR polymorphisms. In a study of 44 wild-type isolates and two laboratory strains of HCMV, we subsequently confirmed the presence of STR length polymorphisms and showed that a multiplexed PCR based on 10 STR regions may allow accurate comparisons of HCMV strains. This application requests support to validate this methodology. We intend to study at least 300 HCMV isolates from Iowa and Texas to determine the precise nature of the STR polymorphisms and their role in analyzing HCMV strains. We will examine three hypotheses regarding STR polymorphisms in HCMV: 1) Many STR polymorphisms exist for HCMV; 2) HCMV STR polymorphisms remain stable during prolonged excretion by individual children and after horizontal transmission among children; and 3) STF polymorphisms provide novel information regarding HCMV evolution. These aims will be accomplished by analyzing HCMV strains using a multiplexed PCR analysis. STR data regarding HCMV strains will be compared against the "gold standard" of nucleotide sequence and RFLP analysis. Characterizing HCM' strains by STR analysis will facilitate future studies of HCMV evolution and will provide a novel means t to fingerprint HCMV strains.